Print quality in B&W laser printers has advanced to the point where dollar-for-dollar the different manufacturers are pretty much indestinguishable. The only difference you might find is the quality (evenness etc...) of the halftones.
The main features you'll want to compare are
- speed (ppm)
- emulation (you'll need PCL5 or 6 and probably PostScript, but PS isn't as important these days now that there is CUPS printing for OS X)
- networking (don't screw around with USB or printer sharing - spend the money to get a networked printer)
- capacity (paper types and cartridge sizes)
- cost of supplies (toners and drums)
- mabe worry about processor (speed/ram) but not so important
I just got a Brother 1570DN for home and it works very well under both OS X and XP over ethernet/wireless. You might want to check forums to review compatibility issues, but generally Brother, HP and Samsung(?) are good at supporting Macs.
For colour, things get a lot more complicated. Make sure you understand the tradeoffs involved with a sub-$1,000 colour laser printer (speed, print quality etc...). Colour lasers simply have not matured to the point of B&W.
Good luck!